Process for the production of high quality carbon black

ABSTRACT

High quality carbon black forming material convertible with high yield into furnace black having a high abrasion resistance in rubber is prepared by dissolving pitch with conventional thinly liquid carbon black feed stock and mechanically separating suspended matter from the mixture obtained.

This is a division of application Ser. No. 962,187 filed Nov. 20, 1978 now U.S. Pat. No. 4,225,416 which is a division of application Ser. No. 735,888 filed Oct. 26, 1977 and now U.S. Pat. No. 4,154,808.

The most important process for the production of carbon black for the rubber, synthetic resin and pigment industries today is the furnace black process. The increasing demands of the tire industry particularly cause a steadily increasing carbon black production. Parallel to the increasing consumption of carbon black there also arises a growing demand for usable carbon black feedstocks. Because of the energy crisis there has arisen a deficiency situation in this area. The process of the present invention widens the base of very high quality carbon black feedstocks.

In the production of furnace black hot combustion gases are produced by burning of a fuel into which there is sprayed a hydrocarbon. In an endothermic reaction the hydrocarbon vaporizes and decomposes into carbon (carbon black) and hydrogen. It has been shown that not all hydrocarbons are suited in an equal measure for the production of carbon black. In principle there exist gaseous, liquid and solid hydrocarbons. The arrangement is somewhat fluid since the temperature has an influence on the state of aggregation. Apart from a few exceptions the liquid carbon black feedstocks have proven as the best suited for the production of furnace black. On account of the low density with gaseous hydrocarbon the carbon concentration per unit of volume is very low. On the contrary with solid hydrocarbons (solid at 100°-200° C.) the conversion into the gas phase, which precedes the formation of carbon black, is too slow.

However, the liquid hydrocarbons also are in no way equally suited for the production of carbon black. In a time of economical use of energy source the carbon black feedstock is preferred which permits under comparable production conditions the highest carbon black yield per unit of time and the highest yield, i.e., per kilogram of carbon black feedstock employed the formation of the largest amount of carbon black. From experience several characteristics have become evident which are able to characterize the value of a carbon black feedstock for the production of carbon black.

One of these characteristics is the specific gravity of the liquid hydrocarbon, which can be easily measured with pycnometers or hydrometers. A further important characteristic is the ratio of carbon atoms to hydroen atoms, in the carbon black feedstock designated for short as the C/H ratio. This ratio can be easily calculated from an elemental analysis of the carbon black feedstock. In Table 1 there are entered both of these characteristics for the normally employed spectrum of typical high quality carbon black feedstocks. Therein the worldwide most frequently employed carbon black feedstocks for the furnace black process are so presented that the value of the liquid carbon black feedstock increases from the top to the bottom. As a measure of this, there can be applied for example the oil yield in processing under the same conditions to carbon black of the same quality. Thus under specifically defined conditions for example there are obtained from 100 kg. of heavy anthracene oil 41 kg. of carbon black, from aromatic concentrate under the same conditions only 25 kg. of the same carbon black.

A higher density and a higher atomic ratio C/H thus is regarded as a measure for the value or the quality of a feedstock for its suitability as carbon black feedstock. Unfortunately the highest quality feedstocks are only available in a limited amount so that frequently it is necessary to reach back to feedstocks in the upper range of Table 1. In order to expand the range of the highest quality carbon black feedstocks, the idea has been pursued to also incorporate pitch to the base from petroleum products and especially to the base from coal tar in the circle of carbon black feedstocks, as well as to incorporate other residue which have acquired a pitch-like character through previous strong thermal treatment.

For comparison below Table 1 there are entered for comparison with the conventional carbon black feedstocks the test data for a coal tar pitch. According to the previous statements this material must be an excellent carbon black feedstock because of its density and its atomic ratio.

                                      TABLE 1                                      __________________________________________________________________________     DENSITY, ELEMENTAL ANALYSIS AND ATOMIC RATIO OF C/H OF                         FAVORABLE CARBON BLACK FEEDSTOCK AND FROM COAL TAR PITCH                       Density Referred to 20° C.                                                             Elemental Analysis in Weight %                                  g/ml           C  H  N  S  O   Ratio of C/H Atoms                              __________________________________________________________________________     Aromatic concentrate*                                                                      0.976                                                                             87.2                                                                              9.2                                                                               0.2                                                                               1.8                                                                               1.6 0.79                                                                              ↑                                      Steamcracked oil light*                                                                    1.035                                                                             91.1                                                                              8.4                                                                               -- 0.1                                                                               0.4 0.91                                                                              Increasing carbon                                                              black feedstock                              Steamcracked oil heaby*                                                                    1.070                                                                             92.1                                                                              7.0                                                                               -- 0.1                                                                               0.9 1.10                                                                              quality                                      Anthracene oil light*                                                                      1.085                                                                             91.0                                                                              6.2                                                                               0.8                                                                               0.6                                                                               1.4 1.22                                                                              ↓                                     Anthracene oil heavy*                                                                      1.136                                                                             91.4                                                                              5.8                                                                               0.8                                                                               0.7                                                                               1.3 1.31                                                                              ↓                                     Coal Tar Pitch                                                                             1.279                                                                             91.9                                                                              4.3                                                                               1.2                                                                               1.0                                                                               1.6 1.78                                            __________________________________________________________________________

To be sure it first separates because it is a conchoidal, hard, refractive material and in this form cannot normally be inserted in the normal furnace black reactors. Here there are now carried on the operating directions to pass the solid state of aggregation by dissolving the pitch, e.g., coal tar pitch in other liquid carbon black feedstocks which are present in sufficient amount and thus to bring it into a form which is better handled.

The following per cent data for the proportions between the materials employed (e.g., steam cracked oil and coal tar pitch) are weight percent.

                  TABLE 2                                                          ______________________________________                                                              Viscosity in cp                                                                at 100° C.                                         ______________________________________                                         light steamcracker oil                                                                         100%            25                                             light steamcracker oil                                                                         80%                                                                                            40                                             coal tar pitch  20%                                                            light steamcracker oil                                                                         60%                                                                                           100                                             coal tar pitch  40%                                                            light steamcracker oil                                                                         40%                                                                                           300                                             coal tar pitch  60%                                                            coal tar pitch  100%           10,000                                          ______________________________________                                    

From preceding Table 2 it can be seen that pure coal tar pitch is too highly viscous to be able to be used in pure form industrially. In comparison, by dissolving the pitch in a thin liquid carbon black feedstock the viscosity can be so strongly reduced that an unobjectionable processing can take place. Thus a mixture of 60% light steam cracked oil and 40% coal tar pitch has no higher viscosity than many conventional carbon black feedstocks. The improved chance of obtaining a high oil yield in the production of the carbon black is easily recognized if both important characteristics, the density and atomic C/H ratio before and after the addition of pitch are compared.

                  TABLE 3                                                          ______________________________________                                                        Density Referred                                                               to 20° C.                                                                           Atomic                                                             g/ml        C/H Ratio                                           ______________________________________                                         light steamcracked oil                                                                          1.035         0.91                                            60% light steamcracked oil                                                                      1.133         1.26                                            40% coal tar pitch                                                             ______________________________________                                    

The mixture shifts according to density and atomic C/H ratio in the range between light and heavy anthracene oil, i.e., the highest quality known carbon black feedstocks.

Experiments were carried out with the described mixtures for the production of carbon black. The carbon black yield per unit amount of feedstock is described in this application as yield. The good yields sought have been reached in using the described mixtures, but the carbon black produced had unexpectedly poor properties. If a rubber mixture is prepared with these carbon blacks, these mixtures fail because of an extraordinarily poor abrasion resistance which lies up to 40% below the value reached by normal carbon black feedstocks. This is the real reason why coal tar pitches as well as other pitches previously could not be employed for the production of carbon black.

The invention points out an unexpected way, using the advantages of higher yield, to obtain carbon black feedstocks which permit the production of high quality carbon black. The object of the invention is the development of a process for the production of high quality feedstocks convertible with high yield into furnace black having high abrasion resistance in rubber which process comprises dissolving the pitch feedstock and mechanically separating suspended materials from the mixture obtained.

This process has nothing to do with the already known separation of coarse inorganic impurities from liquid carbon black feedstocks, as takes place for example to avoid injury to the ceramic walls of the carbon black reactor. The process of the invention generally assumes the separation of substantially larger amounts of material than would be necessary in a purification from customary coarse inorganic impurities. Rather a portion of organic suspended material is ascertained in the opaque, black colored liquid mixture obtained by the solution treatment which is found to be separable by centrifuging or filtering. The last mentioned solution by insertion as the carbon black feedstock furnishes not only good carbon black yields and increased hourly carbon black capacity but additionally an unexpected improvement in quality of the carbon black produced in the form of excellent industrial rubber properties, particularly a very high abrasion resistance in rubber mixtures.

It was also found that the content of suspended material of the pitch/carbon black feedstock mixture generally approximates in relation to the content of the mixture which passes as insoluble material in pure benezene, but occurs by highest chance, because any carbon black feedstock has an individual solvent power for pitch which differs from benzene. The content of benzene insolubles of the mixtures prepared according to the invention can be related to their relative evaluation and to optimization of the process of the invention.

The pitch is first subjected to a solvent action according to the process of the invention. Therein the process is preferably carried out by grinding the pitch after coarse comminution, the pitch powder introduced with stirring to the liquid carbon black feedstock heated to a temperature above 100° C., preferably 100° to 150° C., especially 120° C. and then the solvent action discontinued as soon as the residue free mixture passes a sieve with a mesh width of about 0.4 mm.

The carbon black forming oil (feedstock) should have a relatively low viscosity; at best there is used a carbon black feedstock having a viscosity between 5 and 30 cp.

For the mechanical separation of suspended matter there have primarily been found advantageous the use of centrifuges with number of revolutions per minute between 3,000 and 60,000 according to the diameter of the rotor, preferably 6,000 to 45,000, particularly about 40,000 revolutions/min and filters with an average pore width between 3 and 20μ, preferably 5 to 10μ, particularly around 6μ.

According to the mixing ratio between pitch and carbon black forming oil and the type of the latter, there can be required a heating of the mixture before carrying out the separating step. An approved form of the invention therefore provides subjecting a mixture heated to a temperature between 100° and 170° C. to centrifugation or to filtration.

The conditions for the mechanical separation of the suspended matter can be adapted in a suitable manner to the type and composition of the starting pitch and carbon black feedstock in order to obtain an optimum result, i.e., to produce a yield of a carbon black forming material workable to a qualitatively especially high quality carbon black. This is fundamentally attained if the mechanical separation is so carried in reference to temperature of the mixture, number of revolutions of the centrifuge or pore size of the filter and amount of throughput per unit of time that the product of the process accumulates with a content of benzene insoluble below 0.6 weight %, preferably below 0.2 weight %.

Because of its good suitability, availability and ecconomy there is preferably employed in the process coal tar pitch. As the carbon black forming oil (feedstock) primarily there are used thin liquid steam cracked oils or anthracene oils. According to a variant of the invention there is employed as the mixture to be separated mechanically a thermally cracked carbon black forming oil (feedstock) which already contains some pitch. The step of solvent action is thereby eliminated, the already present pitch/carbon black forming oil (feedstock) mixture can be immediately centrifuged or filtered by observing suitable conditions.

The invention is also directed to the carbon black forming oil (feedstock) obtainable by the pictured process as well as their use for the production of improved furnace blacks, especially with high abrasion resistance when used with rubber.

The process of the invention can comprise, consist essentially of or consist of the steps set forth using the materials set forth.

The advantages obtainable by invention are demonstrated and explained below by the examples.

EXAMPLE 1

There was used a light steam cracked oil with the following test data:

    ______________________________________                                         Density, referred to:                                                                          20° C.                                                                             g/me     1.035                                      Boiling analysis:                                                                               5 Vol%    °C.                                                                              215                                                        10 Vol %   °C.                                                                              228                                                        20 Vol %   °C.                                                                              237                                                        30 Vol %   °C.                                                                              244                                                        40 Vol %   °C.                                                                              260                                                        50 Vol %   °C.                                                                              289                                                        60 Vol %   °C.                                                                              320                                                        70 Vol %   °C.                                                                              331                                                        80 Vol %   °C.                                                                              392                                        Distillation residue                                                                             weight %      11.4                                           Benzene insolubles                                                                               weight %      0.0                                            Elemental analysis:                                                            weight %          carbon        91.1                                                             hydrogen      8.4                                                              nitrogen      --                                                               sulfur        0.1                                                              oxygen        0.4                                            Atomic C/H ratio                0.91                                           ______________________________________                                    

Besides there was used a coal tar pitch with the following test data. Because of the high boiling character, a boiling analysis of the pitch is not possible.

    ______________________________________                                         Density, referred to: 20° C.                                                                g/ml       1.279                                           Softening point:    °C. 70                                              Benzene insolubles: weight %   18.2                                            Elemental analysis:                                                            weight %            carbon     91.9                                                                hydrogen   4.3                                                                 nitrogen   1.2                                                                 sulfur     1.0                                                                 oxygen     1.6                                             Atomic C/H Ratio               1.78                                            ______________________________________                                    

A liquid mixture was produced from 40 weight % coal tar pitch and 60 weight % steam cracked oil. For this purpose the glassy-hard coal tar pitch supplied in pieces having a diameter of 15 to 25 cm. was first ground to particles having a size of 1 to 2 mm. The steam cracked oil was then heated to about 120° C., stirred with a stirrer having 100 to 150 revolutions/min. and then the pulverized coal tar pitch slowly fed in. After stirring for 10 to 15 minutes at the temperature mentioned a sample of the mixture was poured through a sieve having a mesh width of 0.4 mm. There did not remain any pitch particles on the sieve and the solvent action was regarded as concluded. The most important test data of the pitch carbon black feedstock mixture are:

    ______________________________________                                         Density at 20° C.                                                                          g/ml        1.135                                           Benzene insolubles weight %    7.1                                             ______________________________________                                    

Light steam cracked oil and the mixture prepared above were reacted in parallel in small furnace reactor to form carbon black with the same analytical properties. In the production experiments the following operating data was observed and there was obtained carbon black with the stated analytical test data:

    ______________________________________                                                         Light                                                                          Steam- Mixture of Light                                                        cracker                                                                               Steamcracker Oil/                                                       Oil    Coal Tar Pitch                                          ______________________________________                                         Operating and                                                                  Production Data                                                                Total air Nm.sup.3 /h                                                                            21.5     21.5                                                Fuel gas Nm.sup.3 /h                                                                             2.5      2.5                                                 Amount of oil kg/h                                                                               3.96     4.55                                                Amount of carbon black kg/h                                                                      1.28     1.82                                                produced                                                                       yield %           32.3     40.0                                                Properties of the Carbon                                                       Black Produced                                                                 Iodine adsorption          107                                                 According to DIN 53 552 mg/h                                                                     110                                                          Dibutyl phthalate                                                              Number/ASTM D 2414-70 ml/g                                                                       1.21     1.23                                                Color Strength                                                                 According to DIN 53 204                                                                          100      100                                                 pH-Value                                                                       According to DIN 53 200                                                                          6.7      6.6                                                 ______________________________________                                          DIN is the abbreviation for German Industrial Standard.                  

As expected there was reached a substantially high hourly carbon black production with the pitch containing mixture. Also the yield is considerably higher for a carbon black using the mixture which lies at a comparable level in the most important analytical data. Aggravated differences, however, appear if the carbon blacks are incorporated in rubber.

There were used therein the following noted recipes and there were used the operating procedure described in Kautschuk und Gummi, Vol. 19 (1966) No. 8, pages 470-474 and in Vol. 23 (1970) No. 1, pages 7-14 to ascertain the specific quality of the filler.

    ______________________________________                                         Synthetic Rubber Mixture                                                       ______________________________________                                         100 parts by weight    Buna Huls 15 (a styrene-                                                       butadiene copolymer)                                    40 parts by weight     Carbon Black                                            3 parts by weight      Zinc Oxide RS                                           2 parts by weight      Stearic Acid                                            2 parts by weight      Sulfur                                                  1 part by weight       Vulcazit CZ (CBS)                                       ______________________________________                                                                    Mixture of Light                                                               Steamcracker Oil/                                                   Light Steam-                                                                              Coal Tar                                                            cracker Oil                                                                               Pitch 60:40                                         ______________________________________                                         Incubation time t.sub.I sec                                                                    644        746                                                 Velocity constant K.sub.V.sup.I min.sup.-1                                                     196        181                                                 Filler Reciprocal                                                              Effect Constant .sup.α F                                                                 1.99       1.96                                                ______________________________________                                    

Here there is already recognized a tendency to a longer incubation time and slower vulcanization. The aggravated difference to be sure first comes to light in carrying out abrasion tests which document the suitability of the carbon blacks for inclusion in tire mixtures.

    ______________________________________                                                         Relative Abrasion Resistance                                   ______________________________________                                         Standard Carbon Black                                                                            100                                                          Carbon Black Produced From                                                     Light Steamcracked Oil                                                                           124                                                          Carbon Black Produced From                                                     Light Steamcracked Oil/                                                        Coal Tar Pitch 60:40                                                                              87                                                          ______________________________________                                    

In this test there is seen a very great fall off in the most important abrasion test which demonstrates that the carbon black product with pitch is completely unsuitable for wear resistant rubber mixtures.

EXAMPLE 2

Starting from the same basic raw materials as are characterized in Example 1, there was carried out a second series of tests for the production of carbon black. There was a difference, however, that the mixture of 40% coal tar pitch and 60% light steam-cracked oil prepared as in Example 1 was not employed directly but underwent a pretreatment. Therein the mixture heated to 140° C. was sent to a centrifuge which was operated at 40,000 rpm (revolutions per minute). The throughput of the mixture amounted to 15 kg./h. Of the total amount employed, a portion of about 9% was expelled by centrifugal action. The cleaned feedstock (starting material) separated from the expelled portion had the following important data:

    ______________________________________                                         Density at 20° C.                                                                          g/ml        1.133                                           Benzene insolubles weight %    0.18                                            ______________________________________                                    

It was reacted to carbon black for the further investigations in a furnace reactor in comparison to light steam-cracked oil. Therein the following reference data was noted. The analytical data of the carbon black produced are entered below the reference data.

    ______________________________________                                                                   Light                                                                          steamcracked                                                                   oil/coal                                                                       tar pitch                                                              Light steam                                                                            60:40                                                                  cracked oil                                                                            Centrifuged                                          ______________________________________                                         Operating Data                                                                 Total amount of air Nm.sup.3 /h                                                                    21.5      21.5                                             Amount of fuel gas Nm.sup.3 /h                                                                     2.5       2.5                                              Amount of carbon black kg/h                                                                        3.96      4.60                                             feedstock                                                                      Amount of carbon black kg/h                                                                        1.28      1.89                                             Yield %             32.3      41.1                                             Analytical Data                                                                Iodine adsorption                                                              according to DIN 53 552 mg/g                                                                       110       109                                              DBP-Number                                                                     according to ASTM D 2414-70 ml/g                                                                   1.21      1.20                                             Color strength                                                                 according to DIN 53 204                                                                            100       99                                               pH-value                                                                       according to DIN 53 200                                                                            6.7       6.7                                              ______________________________________                                    

As in Example 1 here also there can be recognized the higher carbon black yield and the higher yield with the same level of analytical data for the carbon black produced.

Also in this case the materials were employed in the same test mixture as in Example 1. As important specific rubber data the following data was ascertained:

    ______________________________________                                                                  Carbon                                                                         black                                                                          produced                                                             Carbon    from light                                                           black     steam-                                                               produced  cracker                                                              from      oil/coal tar                                                         light steam-                                                                             pitch 60:40                                                          cracker oil                                                                              Centrifuged                                           ______________________________________                                         Incubation time t.sub.I sec                                                                     644         650                                               Velocity constant K.sub.V.sup.I min.sup.-1                                                      196         197                                               Filler specific                                                                constant αF                                                                               1.99        2.00                                              ______________________________________                                    

The carbon blacks had practically the same test data. The deciding factor was the results of the abrasion test:

    ______________________________________                                                          Relative Abrasion Resistance                                                   in Rubber Mixture                                             ______________________________________                                         Standard Carbon Black                                                                             100                                                         Carbon black produced from light                                               steamcracked oil   124                                                         Carbon black produced from steam-                                              cracked oil/coal tar pitch                                                     60:40 Centrifuged  129                                                         ______________________________________                                    

From these numbers there can be clearly seen the unexpected effect of operating according to the invention. In spite of the higher hourly carbon black output and higher yield there was obtained by the use of the pitch a carbon black with outstanding industrial rubber properties and outstanding resistance to abrasion.

EXAMPLE 3

In this Example there was added the light steam cracked oil of Example 1 and a mixture of 60% steam-cracked oil and 40% coal tar pitch (as described in Example 1). The mixture was subjected to filtration with a filtering apparatus having an average pore size of about 6μ and the filtrate used. The filtrate had the following important test data:

    ______________________________________                                         Density at 20° C.                                                                          g/ml        1.134                                           Benzene insolubles weight %    0.57                                            ______________________________________                                    

The thus prepared product was again added in a comparison to steam cracked oil as carbon black feedstock in the production of carbon black. The operating conditions in the production of the carbon black and the analytical values of the carbon black produced were as follows:

    ______________________________________                                                                   Light                                                                          steamcracked - oil/coal                                                        tar pitch                                                              Light steam                                                                            60:40                                                                  cracker oil                                                                            Filtered                                             ______________________________________                                         Operating Data                                                                 Total amount of air Nm.sup.3 /h                                                                    21.5      21.5                                             Amount of fuel gas Nm.sup.3 /h                                                                     2.6       2.7                                              Amount of carbon black kg/h                                                                        3.84      4.58                                             feedstock                                                                      Amount of carbon black kg/h                                                                        1.25      1.84                                             produced                                                                       Yield %             32.5      40.2                                             Analytical Data                                                                Iodine adsorption                                                              according to DIN 53 5 2 mg/g                                                                       113       104                                              DBP-Number                                                                     according to ASTM D 2414-70 ml/g                                                                   1.26      1.23                                             Color strength                                                                 according to DIN 53 204                                                                            98        97                                               pH-value                                                                       according to DIN 53 200                                                                            6.8       6.4                                              ______________________________________                                    

The industrial rubber tests led to the following results:

    ______________________________________                                                                Light steamcracker                                                    Light steam-                                                                            oil/coal tar pitch                                                    cracker oil                                                                             60:40 Filtered                                          ______________________________________                                         Incubation time t.sub.I sec                                                                    590        550                                                 Velocity constant K.sub.V.sup.I min.sup.-1                                                     180        190                                                 Filler specific                                                                constant αF                                                                              2.08       2.04                                                ______________________________________                                    

In the decisive test of the abrasion resistance in rubber the filtered mixture was shown to be usable.

    ______________________________________                                                          Relative Abrasion Resistance                                                   in Rubber Mixture                                             ______________________________________                                         Standard Carbon Black                                                                             100                                                         Carbon black produced from                                                     Steamcracker oil   123                                                         Carbon black produced from                                                     steamcracker oil/coal tar                                                      pitch 60:40 Filtered                                                                              118                                                         ______________________________________                                    

The abrasion resistance of the carbon black prepared from the filtered coal tar containing mixture was of the same order to magnitude as with that from steam-cracked oil alone, although it appears that the treatment in the centrifuge was somewhat more effective and active.

EXAMPLE 4

The previous examples are based on the preparation of coal tar pitch according to the invention for inclusion in a carbon black feedstock. Coal tar pitch at normal temperatures is solid and glassy. It holds in general for the highest pitch containing pitches, i.e., aromatic condensed products. This example shows that the procedure of the invention can also be used with low pitch products in simple manner.

In the production of gas blacks anthracene oil is vaporized under the influence of temperature, a carrier gas is laden therewith and gas black is produced in the reaction with air in small flames. By the effect of temperature on the anthracene oil in the vaporizer a portion forms high molecular weight material (condensation). Together with the non-vaporizable materials already present in the oil at the vaporizing temperature there results a residue which contains a certain pitch portion (see Ullmann's Enzyklopadie der technischen chemie, Vol 14, page 798 bottom). In contrast to the cases described in Examples 1 to 3, however, this pitch is already diluted with excess anthracene oil so that the diluting step of Examples 1 to 3 is eliminated and a direct separation of portion injuring the quality can take place. There was employed a carbon black feedstock having the following test data:

    ______________________________________                                                                       Gas Black                                                                      Discharge                                                   Heavy   Gas Black  Centrifuged                                                 Anthracene                                                                             Discharge  According to                                                oil     Normal     Example 2                                        ______________________________________                                         Density, referred to                                                           20° C. g/ml                                                                          1.135     1.171      1.176                                        Benzene insolubles                                                             weight %     0.02      0.75       0.03                                         Boiling analysis                                                               up to 5 Vol % °C.                                                                    289       293        304                                          10 Vol % °C.                                                                         306       314        318                                          20 Vol % ° C.                                                                        327       335        339                                          30 Vol % °C.                                                                         335       351        351                                          40 Vol % °C.                                                                         345       362        362                                          50 Vol % °C.                                                                         353       373        372                                          60 Vol % °C.                                                                         362       383        382                                          70 Vol % °C.                                                                         375       410        410                                          80 Vol % °C.                                                                         383       --         --                                           ______________________________________                                    

Carbon black was produced in a small furnace apparatus from heavy anthracene oil, the above defined gas black residue and the same residue after centrifuging according to Example 2. The operating conditions and the analytical properties of the carbon black produced are set forth below:

    ______________________________________                                                        Heavy     Gas Black Gas Black                                                  Anthracene                                                                               Residue   Residue                                     Operating Data Oil       Normal    Centrifuged                                 ______________________________________                                         Total amount of air Nm.sup.3 /h                                                               21.5      21.5      21.5                                        Amount of fuel gas Nm.sup.3 /h                                                                3.6       3.6       3.6                                         Amount of carbon                                                               black feedstock kg/h                                                                          4.68      4.81      4.84                                        Amount of carbon                                                               black produced kg/h                                                                           1.99      2.19      2.22                                        Yield %        42.5      45.5      45.8                                        ______________________________________                                    

    ______________________________________                                                        Heavy     Gas Black Gas Black                                                  Anthracene                                                                               Residue   Residue                                     Analytical Data                                                                               Oil       Normal    Centrifuged                                 ______________________________________                                         Iodine adsorption                                                              according to                                                                   DIN 53 532 mg/g                                                                               125       121       121                                         DBP-Number                                                                     according to                                                                   ASTM D 2414-70 ml/g                                                                           1.27      1.23      1.26                                        Color strength                                                                 according to                                                                   DIN 53 204     97        98        97                                          pH-value                                                                       according to                                                                   DIN 53 200     6.8       6.7       6.5                                         ______________________________________                                    

The industrial rubber tests were carried out with a test mixture corresponding to that in Example 1.

    __________________________________________________________________________                                    Carbon black                                                  Carbon black                                                                            Carbon black                                                                           produced from                                                 produced from                                                                           produced from                                                                          centrifuged                                                   heavy anthracene                                                                        gas black                                                                              gas black                                                     oil      residue residue                                         __________________________________________________________________________     Incubation time t.sub.I sec                                                                  600      620     590                                             Velocity constant K.sub.V .sup.I min.sup.-1                                                  206      200     207                                             Filler specific                                                                Constant αF                                                                            2.17     2.18    2.14                                            __________________________________________________________________________

A clearer distinction is again found in the abrasion data of the carbon black containing rubber mixtures:

    ______________________________________                                                          Relative Abrasion Resistance                                  ______________________________________                                         Standard Carbon Black                                                                             100                                                         Carbon black from heavy coal tar                                               oil (anthracene oil)                                                                              145                                                         Carbon black from gas black                                                    residue            129                                                         Carbon black from centrifuged                                                  gas black residue  140                                                         ______________________________________                                    

Heavy anthracene oil at present is rightly looked at as the highest quality carbon black feedstock. With the gas black residue treated according to the invention the hourly carbon black output and yield is increased about 8-12% compared to heavy anthracene oil, without significantly deteriorating the abrasion resistance. 

What is claimed is:
 1. Carbon black having a high abrasion resistance in rubber compositions prepared by reacting (1) a carbon black forming feedstock prepared by a process consisting essentially of dissolving aromatic pitch in a thin liquid hydrocarbon carbon black feedstock having a viscosity at 100° C. of 5 to 30 cp, there being present suspended matter in the mixture thus formed, mechanically separating suspended matter from the mixture obtained and recovering the pitch containing feedstock having viscosity at 100° C. of 40 to 300 cp with (2) air and (3) a fuel gas.
 2. Carbon black according to claim 1 wherein the thin liquid hydrocarbon feedstock is steam cracked oil or anthracene oil.
 3. Carbon black according to claim 2 wherein the pitch is coal tar pitch.
 4. Carbon black according to claim 1 wherein the pitch used in its-preparation is coal tar pitch.
 5. Carbon black according to claim 4 wherein the carbon black forming material employed to make the carbon black has benzene insolubles below 0.6 weight %.
 6. Carbon black according to claim 1 wherein the carbon black forming material employed to make the carbon black has benzene insolubles below 0.6 weight %.
 7. Carbon black having a high abrasion resistance in rubber compositions prepared by reacting (1) a carbon black forming feedstock prepared by a process consisting essentially of mechanically separating suspended matter from a thermally cracked aromatic pitch containing thin liquid hydrocarbon carbon black feedstock having a viscosity at 100° C. of 40 to 300 cp, there being present suspended matter in the mixture thus formed, the feedstock in the absence of the pitch having a viscosity at 100° C. of 5 to 30 cp, and recovering the pitch containing feedstock with (2) air and (3) a fuel gas.
 8. Carbon black according to claim 7 wherein the thin liquid hydrocarbon feedstock is steam cracked oil or anthracene oil.
 9. Carbon black according to claim 8 wherein the pitch is coal tar pitch.
 10. Carbon black according to claim 7 wherein the carbon black forming material employed to make the carbon black has benzene insolubles below 0.6 weight %.
 11. Carbon black according to claim 7 wherein the pitch is coal tar pitch.
 12. Carbon black according to claim 11, wherein the carbon black forming material employed to make the carbon black has benzene insolubles below 0.6 weight %. 